BAGHDAD, Iraq (CNN) -- A group loyal to terrorist leader Abu Musab al-Zarqawi has "slaughtered" a second American, according to a report posted Tuesday on an Islamist Web site.

The report identified the American as Jack Hensley, a resident of a suburb of Atlanta, Georgia.

U.S. government officials said they have told Hensley's family of the report, but the government has not been able to confirm that Hensley was killed.

A decapitated body has been found in the Baghdad area, but it has not been identified, U.S. officials said.

U.S. officials in Baghdad have Hensley's fingerprints on file for comparison.

Jake Haley, a spokesman for the Hensley family, read a statement saying the family "would especially like to thank the media for the opportunity to speak with the captors of these wonderful men with hopes that we could come to some sort of understanding that did not involve unnecessary death."

"The world has lost exceptional individuals who truly cared about other people's lives and cultures. We are at peace that they are with their Lord," the statement said.

The report of Hensley's killing came a day after the same Web site posted video that showed the beheading of his American colleague, Eugene "Jack" Armstrong.

Armstrong and Hensley were kidnapped September 16, along with Kenneth Bigley of Great Britain.

Al-Zarqawi's group had a stern message for President Bush and British Prime Minister Tony Blair.

"The Muslim blood is not water and the honor of Muslim women won't go to waste. Bush, eat your heart out, and Blair, may you cry with tears of blood. God is great. Glory be to him, his prophet and the faithful," the message said.

The captors have demanded the release of female prisoners held by the U.S. military in two Iraqi prisons.

U.S. officials have said there are no women in the prisons, but two "high-value" female prisoners are being held at an undisclosed location. (Full story)

The group said it killed Hensley after a 24-hour deadline passed without its demands being met. It said the Web site would soon post the video of the killing, "God willing."

"Thank God, the lions of the Tawhid and Jihad have slaughtered the second American hostage at the expiration of the set deadline," the message said. "The British hostage will face the same fate unless the British government does what's necessary to free him."

Hensley's wife, Pati, had made repeated pleas for her husband's life and the lives of his two colleagues.

"These were three gentlemen who had absolutely no agenda other than to enrich the lives of the people they were there to help, and to take their lives would serve no real purpose," she said in an interview Monday.

The men were working on Iraqi reconstruction projects for Gulf Supplies and Commercial Services, a company based in the Middle East.

Before the report of the second killing Tuesday, Bush -- meeting with interim Iraqi Prime Minister Ayad Allawi -- said, "We all stand in solidarity with the [remaining] American that is now being held captive."

Allawi, sitting next to Bush, said, "The barbaric action of yesterday is really unbelievable."

After analysis of Monday's beheading video, a CIA official said there is "high confidence" the voice on the tape is al-Zarqawi's, a Jordanian-born terrorist leader who has ties to Osama bin Laden's al Qaeda network.

The CIA routinely conducts a technical analysis of tapes made public by terrorists, and compares the voice with other samples known to be the person in question.

The voice on the tape "matches" that of al-Zarqawi on other recordings, the official said.

In London, Bigley's brother, Philip Bigley, has asked Blair to take action.

"We feel absolutely helpless," Philip Bigley said.

"We do not have the power to save Ken's life. ... The only person we can now beg to help us is the prime minister. Who else can we ask? There is nobody."

A spokesman in Britain's Foreign Office said Foreign Secretary Jack Straw had spoken with the Bigley family "three or four times, once this morning," but would not go into any details.

Asked about the family's plea for government intervention, the spokesman said that "the government would not change its stance. We do not negotiate with terrorists." U.S. policy is the same.

The group Unification and Jihad, believed to be led by al-Zarqawi, claimed responsibility for killing Hensley and Armstrong. The same group has said it beheaded U.S. businessman Nicholas Berg, South Korean translator Kim Sun-il and two Bulgarian hostages.

Speaking earlier Tuesday, U.S. Secretary of State Colin Powell said Armstrong's death "shows you the nature of the people we are dealing with."

"They are murderers, terrorists who don't want to see the Iraqi people live in peace and freedom and don't want to see their country rebuilt on a democratic base," Powell said.